Aspects and embodiments of the invention are generally directed to piezoelectric actuators, precision moveable stages utilizing the piezoelectric effect, and methods for making the piezoelectric actuators and, more particularly, to monolithic bulk-piezoelectric actuators, precision moveable stages utilizing the monolithic bulk-piezoelectric actuators, and methods for making the monolithic bulk-piezoelectric actuators using direct-write micro-patterning techniques.
Precision piezoelectric stages for linear and rotary motion have proven to be of great value in areas that require accurate and precise positioning and calibration. Ultrasonic motors and piezoelectric actuators utilize actuator constructs such as bimorphs, unimorphs, and shear tubes made of piezoelectric materials such PZT (Lead Zirconate Titanate Oxide).
Piezoelectric materials undergo a change in shape by extension or compression depending on poling directions and electrodes used to provide charges that develop an electric field across the piezoelectric materials. Bimorph actuation is most commonly used to maximize displacement in piezoelectric actuators. Most commercially available bimorphs are made of ceramic piezoelectric materials with thicknesses ranging from 10s of microns to a few millimeters. These piezoelectric materials are often referred to as bulk piezoelectric materials. These actuators are macro-scale, millimeter in thickness, and centimeter in width and length, and are often designed by gluing multiple layers, making them mostly unsuitable for integration in microsystems, where many actuators are required within volumes of mm3 to 1 cm3. Manual assembly of many of these large devices and/or special attention to polarization directions are required for large displacements, which does not lead to small systems, as the manual assembly techniques generally preclude precision placement and repeatable performance across different assembled actuators in one assembly.
Alternatively, thin film MEMS unimorphs and bimorphs use micron-thick piezoelectric material (e.g. PZT, AlN, ZnO) that can result in actuator arrays that can be made in small volumes, in a monolithic manner. Typical thicknesses for the active piezoelectric layer that can be achieved range from nanometers to 10s of microns. The amount of mechanical energy generated by the piezoelectric actuator is proportional to its volume. Hence, the thickness of these structures is too small to produce sufficient forces. Therefore, there is a need for developing thicker piezoelectric actuators, monolithically, to create repeatable, and matched actuators. In light of these shortcomings, others have tried to form monolithic piezoelectric actuators with bulk piezoelectric materials. For example, Aktakka et al. (A 3-DOF piezoelectric micro vibratory stage based on bulk-PZT/silicon crab-leg suspensions, IEEE MEMS. 2013) first polished PZT plates, bonded them to silicon substrates, and then wet etched them to form structures in PZT and silicon. As another example, Kommepalli et al. (Piezoelectric T-beam actuators, ASME J. Mechanical Design, vol. 133, 061003, pp. 1-9, 2011) cut PZT plates using a dicing saw and dry etching to obtain T-structures with six (3 on top and 3 on bottom) electrodes on one beam. This reference develops a structure that enables in-plane and out-of-plane actuation. The dry etching approach requires lithographic patterning and a mask layer. These steps are time-consuming and costly due to the plasma generation system, cost of the gases used, and the need for a cleanroom to manufacture the actuators. It would be cost-effective and commercially attractive to develop a maskless patterning and etching technique in one, to develop and fabricate monolithic piezoelectric actuator arrays. In addition, one can develop approaches to tune the structures for perfect matching across actuators in the same fabrication process.
Focused laser beams are regularly used to cut and drill (laser-micromachining) into ceramic plates including PZT plates. The incorporation of laser cutting to realize planar structures is therefore an attractive method to achieve low-cost, out-of-cleanroom fabrication of actuator arrays.
For the specific application of implementing a motion stage, one often needs to develop pure motion only in one direction. For example, one desires pure rotation or pure linear motion in two directions. If one actuates in one direction, it should lead to minimal motion in the other directions. At the same time one desires to maximize the motion of the stage for a given drive voltage. In the case of a rotary motion, the in-plane motion due to lateral bimorphs generates bending at the interface of the actuators to the stage, which also excites shear motion if directly connected to a rotary stage. Hence, realization of a pure rotary dither motion is a technical challenge not addressed before, and its enablement would be beneficial.
In addition to the actuators, it is often desirable to include capacitors near the stage for buffering and filtering electronic signals. For some electronic sensors and actuators one often needs passive electrical components such as capacitors, resistors, and inductors. It would be advantageous and beneficial to be able to form these components directly, monolithically in PZT using direct write micropatterning.
Piezoelectric devices also include piezoelectric gyroscopes, accelerometers, and energy harvesters. It would be advantageous and beneficial to be able to form these components directly, monolithically in a PZT, co-fabricated with the motion stage, using direct write micropatterning, with the lateral actuator as the elemental component.
In view of the aforementioned shortcomings and problems associated with conventional unimorph and bimorph piezoelectric actuators, and existing approaches to monolithic actuation, the inventors have recognized the advantages and benefits to be realized by addressing these challenges and solving these problems, many of which are realized by the embodied invention directed to monolithic bulk-piezoelectric actuators, precision moveable stages utilizing the monolithic bulk-piezoelectric actuators, and methods for making the monolithic bulk-piezoelectric actuators using direct-write micropatterning techniques, as disclosed and claimed herein below.